1. Field of the Invention
This invention pertains to a surgical procedure for stabilizing the spine. The procedure includes the use of a novel implant. More particularly, this invention pertains to a novel expandable spinal implant and a novel surgical method utilizing the implant.
2. Description of the Prior Art
Chronic low back pain is one of the most common and perplexing problems facing the field of orthopedic surgery. In addition to patient discomfort, chronic low back pain has severe adverse societal impacts, including lost income and possible chronic dependence on drugs, alcohol and public relief programs.
In many cases, low back pain can be avoided by preventing relative motion between spinal vertebrae. This treatment is commonly referred to as intervertebral stabilization. To abate low back pain, stabilization is directed to stabilizing contiguous vertebrae in the lumbar region of the spine.
Surgical techniques are known for use in spinal stabilization. These techniques seek to rigidly join vertebrae which are separated by a degenerated disk. Ideally, the surgery effectively replaces the vertebra-disk-vertebra combination with a single rigid vertebra. Various surgical techniques have been developed which attempt to approach or approximate this ideal.
One technique known in the art is to partially remove a degenerated disk and insert a bone graft into the void formed by the removed disk. Other techniques involve the use of an implant which, acting along or in combination with bone fragments, replace the use of bone grafts. An example of such an implant is shown in U.S. Pat. No. 4,501,269 to Bagby dated Feb. 26, 1989. In Bagby, a large, cylindrical basket is driven into a hole formed between bones which are to be joined. The basket is hollow and is filled with bone fragments which are produced during a boring step. Bone-to-bone fusion is achieved through and about the basket. In Bagby, the hole for the basket is slightly smaller than the diameter of the basket. This structure results in the spreading of the opposing bone segments upon insertion of the basket. This results in taughtness, which provides initial stabilization. Eventual fusion of the opposing bone segments results from bone growth through the basket.
Implants such as those shown in U.S. Pat. No. 4,501,269 are promising. However, improved implant design is necessary to enhance patient safety and the probability of a satisfactory recovery.